Surgical Treatment of a Dens Invagination Type (І) in a Maxillary Lateral Incisor with 6-Year Follow-Up

Dens invagination is a developmental anomaly that requires specific treatment approaches. The invagination is enamel-lined in the crown of the tooth truly negligible, and usually there is no extension on the level of the external amelocemental junction. A well ending surgical root canal treatment of an invaginated tooth with a retrograde filling is presented in this case report. Periapical radiographic examination, after 3 months and 6 years of follow-up, showed periapical healing with osseous formation .


Introduction
Dens invaginatus (DI) is a growing anomaly, which eventuates in an enamel-lined cavity intruding into the crown or root prior to the mineralization phase [1]. The most acceptable etiologic theory is that DI results from an enfolding of the enamel organ (outer portion) into the dental papilla (inner portion) during tooth growth while forming a pocket.
The frequency of DI is reported to be 0.04-10% [2].
Its prevalence is the highest in permanent lateral incisors, central incisors, premolars, canines, and molars in a descending order [3]. It commonly occurs in maxilla rather than mandible, and in permanent instead of deciduous teeth [3]. Bilateral appearance is common in maxillary lateral incisors [4].
The most popular taxonomy was suggested by Oehlers [5], which depicted the anomaly in three categories: Type I: a negligible form of enamel-lined, which does not enlarge over the amelocemental junction but arises within the limits of the crown [6].
Type II: an enamel-lined form attacking the root, which stands restricted as a blind sac. In this form, it is possible to be linked to the dental pulp.
Type III: this form is the one, which penetrates into the root perforating at the apical area showing a 'second foramen' in the apical or in the periodontal area. It does not have an instant link with pulp. The invagination might be completely lined by enamel, but frequently cementum is found lining the invagination [6]. Teeth with DI are prone to early caries and pulp necrosis. Several treatments related to this anomaly are recommended including endodontic therapy or surgery, combined treatment, or extraction [7][8]. Calcium hydroxide has been taken advantage in some cases to induce apical closure and promote repair. Sporadically, the presence of immature roots necessitates apexification [9][10].
Surgical operations can be essential for some cases [11].   acute dentoalveolar abscess or sinus tract [11]. In this report, an Oehlers' Type I invagination was on the maxillary lateral incisor, and the DI was not extended beyond the amelocemental junction. The radiograph showed unilocular well-defined radiolucency.

Case Presentation
Interappointment medicament was considered to compensate the shortcomings of canal preparation. Calcium hydroxide was used for its antimicrobial action and for controlling the exudation of the canal. Then, the canal was obturated with lateral condensation of guttapercha cones and AH-26 sealer after 4 weeks.
A complex procedure is required to treat invaginated teeth. A complicated root canal formation is presented in invaginated teeth, which cannot be instrumented completely. Therefore, they need to be opted for a combination of orthograde and surgical treatment [7,12].
Due to persistent swelling after the second month of follow-up, apical surgery was performed. The surgery provided an additional retrograde seal with ProRoot MTA to the root canal.
Many hypotheses were suggested about the expansion of an invaginated tooth. Following to the deterioration of the dental lamina, a new theory claims that it can be led to fusion, germination, or agenesia. This is also supported by the fact that invagination is most common in maxillary lateral incisors and premolars, the most popular sites of agenesia, and that it occurs in supernumerary teeth [13][14]. An informed consent was obtained from the patient.

Conclusion
The three-month radiograph follow-up showed partial healing of the radicular cyst and the six-year follow-up revealed complete healing.